[Messi]

Hello.

1, my case is about coal combustion. I want to compute the stokes number near the surface of cylinder in a cross flow.

2, In the formula of stokes number (cylinder in a cross flow):

stokes number=(ρp*Dp^2*U）/（9*μg*Dc);
where ρp, particle density; Dp. particle diameter; μg gas flow viscosity; R, cylinder diameter.

3, However, I found that in different papers, the meaning of U are different, such as particle velocity, free stream velocity, gas mainstream velocity or ensemble average particle(and gas) velocity. They are different.

4, my question is: which U should I choose in my computation for stokes number?